xe2x80x9cNot Applicablexe2x80x9d
1. Field of the Invention
This invention relates to lubricants. In particular, it describes non-symmetric, partially fluorinated lubricants and additives, which are soluble in lubricating oils and impart anti-wear and friction-reducing benefits to lubricant formulations.
2. Description of the Prior Art
Two of the most important functions of a lubricant are to reduce friction and to reduce wear on moving parts. Full-film lubrication, where moving parts are always separated by a film of lubricant such that the parts never make contact, is an ideal that cannot always be achieved in practice. Design constraints, together with high load, slow speed, lubricant starvation, or low viscosity of the lubricant, may preclude full-film lubrication and increase the severity of contact. These conditions are often unavoidable during normal operation of machinery, and particularly severe during startup and shutdown.
In cases where full-film lubrication cannot be ensured at all times, anti-wear agents and friction modifiers are usually employed to modify the surfaces to be lubricated. Such anti-wear agents modify these surfaces through adsorption or chemical reaction to form a new surface that can reduce friction and resist wear. Many kinds of anti-wear agents are known. Some of the most widely used and relied upon are the zinc dialkyldithiophosphates (ZDDPs), which find application in many different types of lubricants. Although these compounds have been used for many years in passenger car motor oil, their use is currently restricted (0.1% P vs. 0.12% allowed in the previous GF-1 specification) because the phosphorus from ZDDP poisons catalytic converters, leading to increased emissions. It is anticipated that the future use of ZDDP may be reduced even more than the current level. Anti-wear agents, which can be used in place of ZDDP or in addition to it, are therefore of great interest.
Use of fluorinated and partly-fluorinated materials, as lubricants are known. One limitation of the fluorinated and partly-fluorinated materials previously known is their very low solubility in conventional lubricant base fluids such as natural and synthetic hydrocarbons and esters. Although solid additives may be used in lubricants, they pose several problems. For example, it is known that solid polytetrafluoroethylene (PTFE) can be dispersed in lubricant fluids to reduce friction and wear. However, effectiveness of such a dispersed lubricant depends on maintaining the solid PTFE particles in stable dispersion. Achieving an indefinitely stable dispersion is a challenge, particularly in a formulated lubricant, which may contain detergents, dispersants, or surfactants that may destabilize the PTFE dispersion. Particles of a dispersed solid may flocculate over time in use. Such flocculated particle may then plug or restrict flow of the lubricant in the equipment and result in lubricant starvation in critical locations. The use of soluble additives instead of dispersed solid additives eliminates this problem.
Unfortunately, in the case of PTFE, there is no equivalent material that is soluble in common mineral oil base fluid. Other fluorinated materials have been developed as lubricants, including some liquid highly fluorinated materials such as perfluoropolyethers, but even these liquid highly-fluorinated materials are insoluble in common mineral oil base fluids.
Finally, highly fluorinated materials are significantly more expensive than common lubricant base fluids, making it impractical to use highly fluorinated materials themselves as base fluids except in certain specialized uses where lower cost base fluids are not acceptable.
In the prior art, the terms xe2x80x9cpartly-fluorinatedxe2x80x9d and xe2x80x9cpartially fluorinatedxe2x80x9d can be confusing since they may be used interchangeably, or either one or both terms may used to refer generically to many different types of organic compounds having some but not all of the hydrogen replaced by fluorine substituents. Thus the terms as used in the prior art do not necessarily adequately describe the structure of the molecule in regard to placement of the fluorine substituents.
As used herein the term partly-fluorinated means that both end groups of a molecule are fluorinated to some extent. Partly-fluorinated materials, particularly esters and ethers, have been disclosed as lubricants for magnetic media, for example, Japanese Patent 259482, Japanese Patent 08259501, and U.S. Pat. Nos. 5,578,387; 5,391,814 and 5,510,513.
Japanese Patent 01122026 teaches use of fluorine containing dibasic acid esters derived from diacids up to C8 as lubricants for magnetic media. This publication, as does PCT publication, US/92/0833 1, teaches that the acid structure from which the diester is formed may have double bonds present. The molecular structures taught by each of these publications may also have fluorine atoms present in each of the end group.
Partly-fluorinated adipic acid diesters, Rf(CH2)xO2C(CH2)4CO2(CH2)xRf, have been disclosed as lubricating coatings by Russian patent SU 449925. Bowers et al (Lubr. Eng., July-August, 1956, pages 245-253) studied the boundary lubricating properties of several similar esters. The compounds disclosed in this publication have fluorine present in each of the diester groups, that is the fluorination is symmetric. These partly-fluorinated esters have very low solubility in conventional lubricant base fluids and are therefore, of limited utility as additives in such base fluids.
Japanese Patent 2604186 discloses 1,2,3,4-butane-tetracarboxylic acid tetraesters with partly-fluorinated alcohols, but since all four ester groups are derived from fluorinated alcohols, these esters, too, are symmetric. Other examples of the teaching of symmetrically fluorinated molecular structures include U.S. Pat. Nos. 4,203,856; 5,066,856 and 4,039,301 and in JP08258482 and JP08259501.
Fluorine-containing tri-carbonyl compounds, including some esters, are disclosed as lubricant additives in Japanese patent JP 07242584, and partial fluoroesters of polycarboxylic acids, in which the acid functional groups are not completely esterified was taught in U.S. Pat. No. 3,124,533.
In view of the above description of the prior art, it is an object of the present invention to provide a fluorinated lubricant additive which can serve as an anti-wear agent and friction reducer that is compatible with conventional lubricant base fluids and which overcomes the cost and solubility limitations of highly fluorinated solid and liquid materials. This object has been achieved in non-symmetric, partially fluorinated compositions and compounds of the present invention.
Thus, the present invention provides a composition for use as a lubricant or an additive to a lubricant formulation comprising an organic molecular structure wherein said structure is a non-symmetric, partially fluorinated structure having backbone formed from alkyl groups, aromatic groups or mixtures of alkyl and aromatic groups, at least two functional linkages joining end groups to the backbone and end groups, wherein at least one end group is wholly or partially fluorinated and at least one other end group contains only atoms selected from the group consisting of hydrogen, carbon, nitrogen, oxygen, sulfur, phosphorous and chlorine.
The functional linkages of the present invention contain atoms selected from the group consisting of oxygen, nitrogen, sulfur, and phosphorous. Preferred functional linkages include carboxylic esters, thioesters, sulfonic esters, ureas, thioureas, amides, phosphates, thiophosphates, imines, amines, ethers, thioethers, urethanes, thiourethanes, sulfoxides, and sulfones.
The present invention also provides a process for synthesizing the present composition comprising the steps of:
a) forming a reaction mixture containing components A and B which when reacted form functional linkages wherein A is a mixture of two or more compounds containing at least one reactive functional group selected either from the group consisting of alcohol, mercaptan and amine or from the group consisting of carboxylic acid, acid anhydride, acid chloride, carboxylic ester, nitrile, sulfonyl halide, isocyanate, isothiocyanate, aldehyde, ketone, alkyl halide, phosphoryl halide, thiophosphoryl halide, phosphoric anhydride, and thiophosphoryl anhydride, and further wherein at least one of said compounds of said mixture is a partially fluorinated compound and at least one other of said compound of said mixture is a non-fluorinated compound; and wherein B is a compound containing at least two reactive functional groups which are the same or different and are capable of reacting with the reactive functional groups present in A and said reactive functional groups of B are selected either from the group consisting of alcohol, mercaptan and amine or from the group consisting of carboxylic acid, acid anhydride, acid chloride, carboxylic ester, nitrile, sulfonyl halide, isocyanate, isothiocyanate, aldehyde, ketone, alkyl halide, phosphoryl halide, thiophosphoryl halide, phosphoric anhydride, and thiophosphoryl anhydride; with the proviso: (i) that when the functional groups of either A or B are alcohols, then the functional groups of B or A, respectively, are selected from the group consisting of carboxylic acid, acid anhydride, acid chloride, carboxylic ester, acid anhydride, nitrile, sulfonyl halide, isocyanate, isothiocyanate, phosphoryl halide, thiophosphoryl halide and alkyl halide; (ii) that when the functional groups of either A or B are mercaptans, then the functional groups of B or A, respectively, are selected from the group consisting of acid halide, isocyanate and alkyl halide; and (iii) that when the functional groups of either A or B are amines, then the functional groups of B or A, respectively, are selected from the group consisting of carboxylic acid, acid anhydride, acid chloride, carboxylic ester, isocyanate, aldehyde and ketone; and
b. reacting the mixture to form the functional linkages, and
c. recovering a non-symmetric, partially fluorinated composition having a molecular structure:
R1fxe2x80x94Fxe2x80x2xe2x80x94R2xe2x80x94Fxe2x80x3xe2x80x94R3h
Where: R1f represents a wholly or partially fluorinated C1 to C40 organic residue end group; Fxe2x80x2 and Fxe2x80x3 represent functional linkages which are either alike or different and are selected from the group consisting of carboxylic esters, thioesters, esters, ureas, thioureas, amides, phosphates, thiophosphates, imines, amines, ethers, thioethers, urethanes, thiourethanes, sulfoxides, sulfones, and mixtures thereof; R2 represents the hydrocarbon backbone selected from the group consisting of a C1 to C30 alkyl, cycloalkyl, and aromatic group and mixtures thereof; and R3h represents a non-fluorinated C1 to C40 organic residue end group.
The preferred structures for component A useful in the present invention include the following, where X represents an xe2x80x94OH, xe2x80x94SH, xe2x80x94NH2 or xe2x80x94NHRxe2x80x2 group:
F(CF2)xCH2X; H(CF2)xCH2X, wherein x is 1 to about 20; mixtures of the telomers of F(CF2CF2)xCH2CH2X wherein x is 1 to about 10 and preferably having an average x of from about 3.5 to about 3.9; mixtures of the telomers of F(CF2CF2)x(CH2CH2O)yH, wherein x is 1 to about 10 and y is 1 to 20 and preferably having an average x of about 3.9 and an average y of about 8, and of the telomers of F(CF(CF3)CF2O)xCF(CF3)CH2X, wherein x is 1 to about 12 and preferably having an average x of about 6.7.
The preferred structures for component B useful in the present invention include the difunctional carboxylic acid, acid anhydride, acid chloride, carboxylic ester, nitrile, sulfonyl halide, isocyanate, isothiocyanate, aldehyde, ketone, alkyl halide, phosphoryl halide, thiophosphoryl halide, phosphoric anhydride, and thiophosphoryl anhydride.
Diacids useful in the present invention include those having from about 4 to 24 carbons, the corresponding acid anhydrides and dimer acids having up to 36 carbons. Acid halides, sulfonyl halides, isocyanates, isothiocyanates, phosphoryl halides and thiophosphoryl halides having structures corresponding to these diacids are also useful in the present invention. Although the preferred structures of the compounds of the present invention are the structures having like functional groups, structures may have mixed functional groups, for example, carboxylic acid/sufonyl halide, carbonyl/carboxylic acid or other combinations.
The present invention includes a lubricant composition comprising a base fluid mixed with the non-symmetric, partially fluorinated compounds of the present invention.